Among conventional internal combustion engines, there is one type of engine which operates with a lean mixture, or achieves what is called lean combustion. This system reduces the occurrence of harmful components in exhaust gases while increasing a fuel efficiency.
However, an excessively lean mixture is likely to generate a misfire because such a lean mixture causes a failure of combustion in a combustion chamber, from which unburned gases flow toward an air-discharging system. The resulting misfire is a factor contributing to the degradation or failure of the function of a catalyst body and the like. The misfire is also a factor contributing to air pollution as a result of the unburned gases being discharged in the air. For such reasons, a fuse sensor is positioned on a downstream side of the catalyst body. The fuse sensor detects a temperature state of the catalyst body when the misfire elevates the temperature of the catalyst body above a predetermined value. At this time, a meter appears, or a warning lamp on a panel turns on, so as to signal a vehicle driver that the misfire has occurred.
Published Japanese Patent Application Laid-Open No. 5-202801 discloses a misfire-determining controller for the aforesaid internal combustion engine. The misfire-determining controller taught by this publication determines an output level of an air-fuel ratio-detecting means, whereby an after-the-sale service engineer can easily diagnose the cause of a misfire in a particular cylinder when inspecting a misfired vehicle. That is, the service technician does not need to check all of the causes of misfires in both fuel injection and ignition systems for each cylinder. In this way, the controller is designed to provide fewer inspection man-hours and less inspection time.
In conventional misfire-determining controllers for internal combustion engines, there are cases where the engine is misjudged to be misfired although the engine normally runs without experiencing any misfire. The misjudgment turns on a lamp, which brings about an inconvenience in that a vehicle driver experiences a feeling of uneasiness and unnecessary confusion as well.
In addition, when the internal combustion engine is used under various situations, misfires may be detected as a result of other causes in spite of the engine being in normal operation.
Such misfires are detected, for example, in the event of: a fuel failure or what is called a gas-free state; a failure of an ISC valve; the presence of an abnormality in a fuel system; or, vehicular adjustment which includes ignition timing, an ISC valve flow rate, a fuel feedback (F/B) correction amount, bypassing air, and the like.
As a result, when misfire determination is made according to conventional misfire monitoring, it is judged as a result of the aforementioned various causes that the engine is in a misfired state. In this case, there are inconveniences, which are disadvantageous in view of practical use, in that the cause of the misfire is difficult to trace, and that additional working time and man-hours are required for locating the cause of the misfire.
In order to obviate the above-described inconveniences, the present invention provides a misfire-determining controller for an internal combustion engine, including a control means which controls so as to execute misfire monitoring for determining a misfire on the basis of variations in an operating state of the internal combustion engine, comprising the improvement wherein the control means is provided with the added function of controlling so as to cease the misfire monitoring when at least one of cases of misfire detection-ceasing conditions is met, the misfire detection-ceasing conditions including the cases of: ignition timing being under adjustment; throttle-bypassing air being under adjustment; an ISC valve flow rate being under adjustment; a fuel feedback correction amount being under adjustment; an abnormality being present in a fuel system; and a fuel failure.
According to the present invention having the above structure, when one of the cases of the misfire detection-ceasing conditions is true, the control means ceases the misfire monitoring. When none of the cases of the misfire detection-ceasing conditions are met, it follows that the control means eliminates the misfire detection-ceasing conditions which cause the misfire. This feature facilitates the tracing of the cause of the misfire at the time of misfire determination, and provides less working time and fewer working man-hours.